Ink jet printing method

ABSTRACT

An ink jet printing method, comprising the steps of: 
     A) providing an ink jet printer that is responsive to digital data signals; 
     B) loading said printer with an ink jet recording element comprising a support having thereon an image-receptive layer capable of accepting an ink jet image; 
     C) loading said printer with an ink jet ink composition comprising water, a humectant and a water-soluble pyrazoleazoindole dye; and 
     D) printing on said ink jet recording element using said ink jet ink in response to said digital data signals.

CROSS REFERENCE TO RELATED APPLICATION

Reference is made to commonly assigned, co-pending U.S. patentapplication Ser. No. 09/689,184 by Evans et al., filed concurrentlyherewith entitled “Dye For Ink Jet Ink”; the disclosure of which ishereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to an ink jet printing method using apyrazoleazoindole dye as a colorant in an ink jet composition.

BACKGROUND OF THE INVENTION

Ink jet printing is a non-impact method for producing images by thedeposition of ink droplets in a pixel-by-pixel manner to animage-recording element in response to digital signals. There arevarious methods which may be utilized to control the deposition of inkdroplets on the image-recording element to yield the desired image. Inone process, known as continuous ink jet, a continuous stream ofdroplets is charged and deflected in an imagewise manner onto thesurface of the image-recording element, while unimaged droplets arecaught and returned to an ink sump. In another process, known asdrop-on-demand ink jet, individual ink droplets are projected as neededonto the image-recording element to form the desired image. Commonmethods of controlling the projection of ink droplets in drop-on-demandprinting include piezoelectric transducers and thermal bubble formation.Ink jet printers have found broad applications across markets rangingfrom industrial labeling to short run printing to desktop document andpictorial imaging.

The inks used in the various ink jet printers can be classified aseither dye-based or pigment-based. A dye is a colorant, which isdissolved in the carrier medium. A pigment is a colorant that isinsoluble in the carrier medium, but is dispersed or suspended in theform of small particles, often stabilized against flocculation andsettling by the use of dispersing agents. The carrier medium can be aliquid or a solid at room temperature in both cases. Commonly usedcarrier media include water, mixtures of water and organic co-solventsand high boiling organic solvents, such as hydrocarbons, esters,ketones, etc.

The choice of a colorant in ink jet systems is critical to imagequality. For colors such as cyan, magenta, yellow, green, orange, etc.,the peak wavelength (λ-max), the width of the absorption curve and theabsence of secondary absorptions are important. The colorant should alsohave a high degree of light fastness after printing onto theink-receiving element. For aqueous dye-based inks, the dye needs to besufficiently soluble in water to prepare a solution that is capable ofproducing adequate density on the receiving element and stable forextended periods of storage without precipitation. High quality ink jetprinting with dye-based inks requires dyes which will provide bothbright hue and good light stability. It is difficult to find dyes,particularly yellow dyes, which meet all of these requirements.

Aqueous dye-based inks for high-quality, photo-realistic, ink jetprinting require water-soluble dyes with excellent color and high light-and water-fastness. Typically the dyes are chosen from acid, direct andreactive dyestuffs developed for the dyeing of natural fibers such aspaper, wool and cotton. Water solubility of these dyes is due to theincorporation of negatively charged substituent groups such as sulfo orcarboxy.

U.S. Ser. No. 09/306,121, now U.S. Pat. No. 6,174,356 filed May 6, 1999,discloses water-soluble azoindole dyes for use in ink jet printingincluding dyes derived from diazotizable heteroaromatic amines. However,there is a problem with some of these dyes in that they do not havesufficient light stability.

U.S. Pat. No. 4,685,934 describes water-soluble pyrazoleazoindole yellowand orange dyes useful for conventional dyeing of synthetic fibers andtextiles. However, there is no disclosure in this patent for use ofthese dyes in ink jet printing.

It is an object of this invention to provide an ink jet printing methodusing bright, readily water-soluble and light stable azoindole dyesderived from diazotizable heteroaromatic amines useful for aqueous inkjet printing.

SUMMARY OF THE INVENTION

This and other objects are achieved in accordance with this inventionwhich relates to an ink jet printing method, comprising the steps of:

A) providing an ink jet printer that is responsive to digital datasignals;

B) loading said printer with an ink jet recording element comprising asupport having thereon an image-receptive layer capable of accepting anink jet image;

C) loading said printer with an ink jet ink composition comprisingwater, a humectant and a water-soluble pyrazoleazoindole dye; and

D) printing on said ink jet recording element using said ink jet ink inresponse to said digital data signals.

DETAILED DESCRIPTION OF THE INVENTION

In a preferred embodiment of the invention, the pyrazoleazoindole dyesemployed in the invention may be represented by the following structure:

wherein:

R₁ and R₃ each independently represents hydrogen, a substituted orunsubstituted alkyl group of 1-6 carbon atoms, a substituted orunsubstituted allyl group, a substituted or unsubstituted aryl group of6-10 carbon atoms, a substituted or unsubstituted heteroaryl group of5-10 atoms or a polyoxyalkylene group of 2-20 alkylene oxide residues;

R₂, X and Y each independently represents the groups listed above forR₁, halogen, cyano, carboxy, acyl, nitro, sulfo, a substituted orunsubstituted alkoxy group of 1-6 carbon atoms, a substituted orunsubstituted aryloxy group of 6-10 carbon atoms, a substituted orunsubstituted alkoxy- or aryloxy-carbonyl group of 1-10 carbon atoms, apolyoxyalkylene group of 2-20 alkylene oxide residues, a ureido group,carbamoyl, a substituted or unsubstituted alkyl-, arylalkyl-, aryl-,diaryl- or dialkyl-carbamoyl group of 1-20 carbon atoms, sulfamoyl, asubstituted or unsubstituted alkyl-, arylalkyl-, aryl-, diaryl- ordialkyl-sulfamoyl group of 1-20 carbon atoms, acylamino, sulfonylamino,amino, or a substituted or unsubstituted alkyl-, aralkyl-, aryl-,diaryl- or dialkyl-amino group of 1-20 carbon atoms;

n represents an integer from 1-4; and

Z represents cyano, carboxy, sulfo, alkoxycarbonyl, carbamoyl or asubstituted or unsubstituted alkyl-, arylalkyl-, aryl-, diaryl- ordialkyl-carbamoyl group of 1-20 carbon atoms;

with the proviso that the dye must contain at least one group capable ofimparting water solubility at a pH of about 4-9.

In a preferred embodiment of the invention, R₁ in the above formularepresents hydrogen, methyl or 2-carboxyethyl. In another preferredembodiment, R₂ represents methyl or phenyl. In still another preferredembodiment, X represents hydrogen, sulfo, a substituted1,3,5-triazinylamino group or an N-alkylphthalamido group. In yetanother preferred embodiment, R₃ represents 4-sulfophenyl,2,5-bis-sulfophenyl, methyl, phenyl, 4-carboxyphenyl or 3-sulfopropyl.In yet another preferred embodiment, Y represents hydrogen. In still yetanother preferred embodiment Z represents cyano, carboxy or carbamoyl.

In the above definition, examples of a substituted or unsubstitutedalkyl group include methyl, ethyl, isopropyl, hydroxyethyl,3-sulfopropyl and m-carboxybenzyl. Examples of a substituted orunsubstituted aryl group include phenyl, naphthyl, 3,5-biscarboxyphenyland 4-sulfophenyl. Examples of a substituted or unsubstituted heteroarylgroup include pyridyl, imidazolyl and quinolyl. Examples of halogeninclude chloro, fluoro, bromo and iodo. Examples of an acyl groupinclude acetyl and 4-sulfobenzoyl. Examples of a substituted orunsubstituted alkoxy group include methoxy, 3-carboxypropoxy and2-hydroxyethoxy. Examples of a substituted or unsubstituted aryloxygroup include phenoxy, 3-carboxyphenoxy and 4-sulfophenoxy. Examples ofa substituted or unsubstituted alkoxy- or aryloxy-carbonyl group of 1-10carbon atoms include methoxycarbonyl, ethoxycarbonyl,2-methoxyethoxycarbonyl and 3-sulfophenoxycarbonyl. Examples of asubstituted or unsubstituted alkyl- aralkyl-, aryl-, diaryl-or dialkylcarbamoyl group include N-methylcarbamoyl,N-methyl-N-4-sulfophenyl-carbamoyl, N,N-bis(4-carboxyphenyl)carbamoyl.Examples of a substituted or unsubstituted alkyl- aralkyl-, aryl-,diaryl-or dialkyl sulfamoyl group include N-methylsulfamoyl,N-methyl-N-phenyl-sulfamoyl, N-(p-sulfophenyl)sulfamoyl andN,N-bis(4-carboxyphenyl)sulfamoyl. Examples of an acylamino groupinclude acetamido, methoxyethylacetamido and 3-carboxybenzamido.Examples of a ureido group include N-methylureido, ureido andN,N′-dimethylureido. Examples of a sulfonylamino group includemethanesulfonamido, p-toluenesulfonamido and 2-sulfatoethanesulfonamido.Examples of a substituted or unsubstituted alkyl- aralkyl-, aryl-diaryl- or dialkylamino group include methylamino, N,N-dimethylamino,methoxy-ethylamino and 3-sulfoanilino.

Examples of groups capable of imparting water solubility at a pH ofabout 4-9 include sulfonic, sulfinic, phosphonic, phosphoric andcarboxylic acid moieties and salts thereof; primary, secondary andtertiary amino groups; and quaternary ammonium or phosphonium groups.

The dyes employed in the invention are not new and may be prepared bythe methods disclosed in the above references or in Dyes and Pigments,Vol 2, pp. 305-318 (1981).

Representative examples of the pyrazoleazoindole dyes employed in thisinvention are listed below.

Dye R₁ R₂ R₃ X Z 1 C₂H₄CO₂H C₆H₅ CH₃ H CN 2 H C₆H₅ H SO₃ ⁻Na⁺ CN 3C₂H₄CO₂H C₆H₅ H H CN 4 C₂H₄CO₂H CH₃ CH₃ H CN 5 CH₂CO₂H CH₃ CH₃ H CN 6CH₃ CH₃

H CN 7 C₂H₄CO₂H CH₃

H CN 8 C₂H₄CO₂H CH₃

H CN 9 H CH₃

H CN 10 CH₃ CH₃

SO₃ ⁻Na⁺ CONH₂ 11 C₂H₄CO₂H CH₃

H CO₂H

Other dyes employed in this invention include:

In general, the above dyes comprise from about 0.2 to about 8%,preferably from about 1 to about 5% by weight of the ink jet inkcomposition.

A humectant is employed in the ink jet composition employed in theinvention to help prevent the ink from drying out or crusting in theorifices of the printhead. Examples of humectants which can be usedinclude polyhydric alcohols, such as ethylene glycol, diethylene glycol,triethylene glycol, propylene glycol, tetraethylene glycol, polyethyleneglycol, glycerol, 2-methyl-2,4-pentanediol, 1,2,6-hexanetriol andthioglycol; lower alkyl mono- or di-ethers derived from alkyleneglycols, such as ethylene glycol mono-methyl or mono-ethyl ether,diethylene glycol mono-methyl or mono-ethyl ether, propylene glycolmono-methyl or mono-ethyl ether, triethylene glycol mono-methyl ormono-ethyl ether, diethylene glycol di-methyl or di-ethyl ether, anddiethylene glycol monobutylether; nitrogen-containing cyclic compounds,such as pyrrolidone, N-methyl-2-pyrrolidone, and1,3-dimethyl-2-imidazolidinone; and sulfur-containing compounds such asdimethyl sulfoxide and tetramethylene sulfone. A preferred humectant forthe composition employed in the invention is diethylene glycol,glycerol, or diethylene glycol monobutylether.

Water-miscible organic solvents may also be added to the aqueous inkemployed in the invention to help the ink penetrate the receivingsubstrate, especially when the substrate is a highly sized paper.Examples of such solvents include alcohols, such as methyl alcohol,ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol,sec-butyl alcohol, t-butyl alcohol, iso-butyl alcohol, furfuryl alcohol,and tetrahydrofurfuryl alcohol; ketones or ketoalcohols such as acetone,methyl ethyl ketone and diacetone alcohol; ethers, such astetrahydrofuran and dioxane; and esters, such as, ethyl lactate,ethylene carbonate and propylene carbonate.

Surfactants may be added to adjust the surface tension of the ink to anappropriate level. The surfactants may be anionic, cationic, amphotericor nonionic.

A biocide may be added to the composition employed in the invention tosuppress the growth of micro-organisms such as molds, fungi, etc. inaqueous inks. A preferred biocide for the ink composition of the presentinvention is Proxel® GXL (Zeneca Specialties Co.) at a finalconcentration of 0.0001-0.5 wt. %.

The pH of the aqueous ink compositions employed in the invention may beadjusted by the addition of organic or inorganic acids or bases. Usefulinks may have a preferred pH of from about 2 to 10, depending upon thetype of dye being used. Typical inorganic acids include hydrochloric,phosphoric and sulfuric acids. Typical organic acids includemethanesulfonic, acetic and lactic acids. Typical inorganic basesinclude alkali metal hydroxides and carbonates. Typical organic basesinclude ammonia, triethanolamine and tetramethylethlenediamine.

A typical ink composition employed in the invention may comprise, forexample, the following constituents by weight: colorant (0.2-8%), water(20-95%), a humectant (5-70%), water miscible co-solvents (2-20%),surfactant (0.1-10%), biocide (0.05-5%) and pH control agents (0.1-10%).

Additional additives which may optionally be present in the ink jet inkcomposition employed in the invention include thickeners, conductivityenhancing agents, anti-kogation agents, drying agents, and defoamers.

In the ink jet printing method of the invention, liquid ink drops areapplied in a controlled fashion to an ink receptive layer substrate, byejecting ink droplets from a plurality of nozzles or orifices of theprint head of an ink jet printer.

Ink-receptive substrates useful in ink jet printing are well known tothose skilled in the art. Representative examples of such substrates aredisclosed in U.S. Pat. Nos. 5,605,750; 5,723,211; and 5,789,070 and EP813 978 A1, the disclosures of which are hereby incorporated byreference.

The following examples illustrate the utility of the present invention.

EXAMPLES

The following control dyes were evaluated as comparative examples:

Dye R₁ R₂ R₃ X Y Z C-1 H C₆H₅ C₆H₅ SO₃ ⁻Na⁺ CH₃ H C-2 H CH₃

H C₆H₅ H C-3 C₂H₄CO₂H C₆H₅

H C₆H₅ H

Preparation of Inks

Inks containing the dyes employed in the invention and control dyes wereprepared by dissolving an appropriate amount of the dye in deionizedwater containing humectants of diethylene glycol and glycerol, each at 6wt. %, a biocide, Proxel GXL® at 0.003 wt. % and a surfactant, Surfynol465® (Air Products Co.) at 0.5 wt. %. The pH of each ink was adjusted toapproximately 8 by adding triethanolamine. The dye concentrations werebased on solution absorption spectra and chosen such that the final ink,when diluted 1:1000, would yield a transmission optical density ofapproximately 1.0. Details are given in the Table below.

TABLE 1 Ink Dye Wt. % Dye 1 1 1.83 2 2 2.9 3 3 2.12 4 4 1.39 5 5 1.32 66 2.53 7 7 1.95 8 8 1.68 9 9 2.56 10 10 3.43 11 11 2.16 12 12 3.45 13 133.66 14 14 4.19 15 15 3.67 16 16 3.37 C-1 C-1 2.9 C-2 C-2 2.14 C-3 C-32.58

Printing of Test Images

The above inks were then filtered through a 0.45μpolytetrafluoroethylene filter and placed in a clean Hewlett-Packard inkcartridge No. HP 51629A and fitted into the black ink station of aHewlett-Packard DeskJet 600® printer. A test image consisting of aseries of 21 variable density patches, approximately 15 by 13 mm insize, ranging from 5% dot coverage to 100% dot coverage was printed ontocommercially-available Kodak Premium Picture Paper for Inkjet, CatalogNo. 824-5276, and allowed to dry for 24 hours at ambient temperature andhumidity.

Evaluation of Test Images

The printed images were bright yellow to yellow-orange in color. TheStatus A blue reflection densities of the maximum density patch (BlueD-max) of the above stepped images were measured using an X-Rite® 820densitometer and are listed in the Table below. Values greater thanabout 1.3 are acceptable.

The stepped images were then subjected to light fade under 50 Kluxhigh-intensity daylight irradiation and 50% relative humidity conditionsfor 2 weeks. The Status A blue densities of the stepped images wereremeasured and the % Status A blue density loss for the 75% dot coveragepatches were calculated. Smaller % loss numbers represent more stabledyes and are preferred.

TABLE 2 Ink Blue D-max % Loss Light Fade 1 1.79 0 2 1.75 24 3 1.5 35 41.81 0 5 1.88 0 6 2.01 10 7 1.87 7 8 1.75 10 9 1.53 0 10 1.77 28 11 1.4142 12 1.38 11 13 1.86 15 14 1.59 14 15 2.0 22 16 1.73 25 C-1 1.83 73 C-21.42 84 C-3 1.6 82

The above data shows that inks containing the dyes employed in theinvention yield more light stable images than closely related analogs.The printed images are also bright and of high density.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

What is claimed is:
 1. An ink jet printing method, comprising the stepsof: A) providing an ink jet printer that is responsive to digital datasignals; B) loading said printer with an ink jet recording elementcomprising a support having thereon an image-receptive layer capable ofaccepting an ink jet image; C) loading said printer with an ink jet inkcomposition comprising water, a humectant and a water-solublepyrazoleazoindole dye; and D) printing on said ink jet recording elementusing said ink jet ink in response to said digital data signals; whereinsaid water-soluble pyrazoleazoindole dye may be represented by thefollowing structure:

wherein: R₁ and R₃ each independently represents hydrogen, a substitutedor unsubstituted alkyl group of 1-6 carbon atoms, a substituted orunsubstituted allyl group, a substituted or unsubstituted aryl group of6-10 carbon atoms, a substituted or unsubstituted heteroaryl group of5-10 atoms or a polyoxyalkylene group of 2-20 alkylene oxide residues;R₂, X and Y each independently represents the groups listed above forR₁, halogen, cyano, carboxy, acyl, nitro, sulfo, a substituted orunsubstituted alkoxy group of 1-6 carbon atoms, a substituted orunsubstituted aryloxy group of 6-10 carbon atoms, a substituted orunsubstituted alkoxy- or aryloxy-carbonyl group of 1-10 carbon atoms, apolyoxyalkylene group of 2-20 alkylene oxide residues, a ureido group,carbamoyl, a substituted or unsubstituted alkyl-, arylalkyl-, aryl-,diaryl- or dialkyl-carbamoyl group of 1-20 carbon atoms, sulfamoyl, asubstituted or unsubstituted alkyl-, arylalkyl-, aryl-, diaryl- ordialkyl-sulfamoyl group of 1-20 carbon atoms, acylamino, sulfonylamino,amino, or a substituted or unsubstituted alkyl-, aralkyl-, aryl-,diaryl- or dialkyl-amino group of 1-20 carbon atoms; n represents aninteger from 1-4; and Z represents cyano, carboxy, sulfo,alkoxycarbonyl, carbamoyl or a substituted or unsubstituted alkyl-,arylalkyl-, aryl-, diaryl- or dialkyl-carbamoyl group of 1-20 carbonatoms; with the proviso that the dye must contain at least one groupcapable of imparting water solubility at a pH of about 4-9.
 2. Themethod of claim 1 wherein R₁ represents hydrogen, methyl or2-carboxyethyl.
 3. The method of claim 1 wherein R₂ represents methyl orphenyl.
 4. The method of claim 1 wherein X represents hydrogen, sulfo, asubstituted 1,3,5-triazinylamino group or an N-alkylphthalamido group.5. The method of claim 1 wherein R₃ represents 4-sulfophenyl,2,5-bis-sulfophenyl, methyl, phenyl, 4-carboxyphenyl or 3-sulfopropyl.6. The method of claim 1 wherein Y represents hydrogen.
 7. The method ofclaim 1 wherein Z represents cyano, carboxy or carbamoyl.
 8. The methodof claim 1 wherein said humectant is diethylene glycol, glycerol ordiethylene glycol monobutylether.
 9. The method of claim 1 wherein saiddye comprises about 0.2 to about 8% by weight of said inkjet inkcomposition.